1. Field of the Invention
The present invention relates to a thermosensitive adhesive composition which is not adhesive at room temperature but becomes adhesive upon application of heat and continues to be adhesive and especially has a sufficient adhesibility to a rough surface adherend, for example, a corrugated board, and a corresponding manufacturing method and a corresponding thermosensitive adhesive material.
2. Discussion of the Background
As adhesive sheets, for example, adhesive labels, seals and stick-ons, typical examples are: (1) a material in which an adhesive agent is applied to release paper and the resultant is attached to a substrate (for example, quality paper, art paper, polyethylene terephthalate (PET) and (2) a material in which an adhesive agent is directly applied to a substrate, release paper is laminated and seal printing is performed. In such adhesive sheets, release paper is required to protect the adhesive agent layer. When release paper is not used, a special coating treatment is necessary for the adhesive agent layer.
Delayed tack type adhesive sheets have appeared in place of such adhesive sheets. Since an adhesive agent for use in this delayed tack type adhesive sheet is not adhesive at room temperature and can be directly applied to an adherend (substrate), release paper, etc., are not required. When compared with typical adhesive sheets, the delayed tack type adhesive sheet is cost-reductive and resource-saving. Consequently, the demand on the delayed tack type adhesive sheet is rapidly increasing in the package material field and other various kinds of fields.
In general, in the adhesive agents for use in the delayed tack type adhesive sheet mentioned above, an adhesiveness imparting agent for imparting the adhesibility to various kinds of substrates is added in a thermoplastic resin and, in addition, a solid plasticizing agent is also added therein. When this kind of the adhesive agent for use in the delayed tack type sheet is heated, the solid plasticizing agent is melted first. Next, the thermoplastic resin and the adhesive imparting agent are dissolved in each other in the melted solid plastic agent functioning as a solvent. This is considered to be the way the adhesibility appears.
However, in the case of the delayed tack type adhesive agent mentioned above, a phenomenon referred to as “blocking” easily occurs in which the delayed tack type adhesive agent is adhesive even when the delayed tack type adhesive agent is not heated (for example, preserved at ambient temperature, for example, 22° C.), which leads to attachment of adhesive layers to each other. This causes a problem when the sheets are labeled.
This “blocking” occurring in the case of such a delayed tack type adhesive agent can be improved to a certain degree when a solid plasticizing agent having a high melting point is used. For example, in published unexamined Japanese patent applications Nos. (hereinafter referred to as JOP) 2003-206455 and 2002-38123, a delayed tack type adhesive agent in which benzophenone is used as a solid plasticizing agent is described. This adhesive agent has adhesibility to a mirror surface, for example, polyolefin and glass, but has weak adhesibility to a rough surface adherend, for example, a corrugated board. When the adhesive agent is attached to a corrugated board, the adhesibility decreases overtime, which creates a great problem when used in logistics, for example, home-delivery service. Furthermore, there is another problem that “blocking” occurs in an environment at 60° C.
In addition, in JOP 2002-105414, a thermosensitive adhesive material is described which contains a hindered phenol compound, a benzotriazole compound, and an aromatic sulfonic amide compound and furthermore, hollow particles having a hollow ratio of 50% in an undercoating layer. However, even when the thermosensitive adhesive material described therein is used, the adhesibility and blocking property are not sufficiently satisfactory for a rough surface adherend, for example, a corrugated board.
In addition, in Japanese patent No. (hereinafter referred to as JP) 3556414, a delayed tack glue is described in which benzotriazole is used as a solid plasticizing agent. The delayed tack glue described therein has a relatively excellent anti-blocking property and can stably sustain the adhesibility over an extended period of time for an adherend formed of, for example, materials such as paper, glass and metal and polyolefin resins such as polypropylene and polyethylene. However, even in the case of the delayed tack glue, the adhesibility for a rough surface adherend, for example, a corrugated board, is weak. Therefore, when the delayed tack glue is attached to a corrugated board, the adhesibility deteriorates over time. Especially, the adhesibility thereof is insufficient in a low temperature environment of not higher than 5° C.
To solve these problems, as a method of improving the adhesibility at a low temperature, for example, combining a liquid plasticizing agent having a low molecular weight is described in JOP 2002-121532. However, this proposal involves a problem in that the liquid plasticizing agent having a low molecular weight transfers to the surface over time, which easily causes blocking.
In addition, as a method of improving anti-blocking property, for example, JOPs H07-3239, 2002-97444, 2002-121533 and H06-172725 describe methods in which a liquid plasticizing agent having a low molecular weight is encapsulated in a microcapsule. However, in these methods, the wall material of the microcapsule has adhesion inhibition after thermal activation, which leads to a problem in that a sufficient adhesibility is not obtained.
In addition, JOP 2003-216047 describes a method in which the adhesibility of an applied material is improved by delaying the recrystallization of the solid plasticizing agent by an application of a liquefied softening agent before and/or after the thermal activation. However, in this method, it is necessary to apply a liquefied softening agent having a low molecular weight, which causes a problem of practical use of the delayed tack agent.
In addition, JOPs 2002-173662, 2003-96408 and 2002-265896 describe a thermosensitive adhesive material having an excellent adhesibility at a low temperature environment. According to these teachings, the adhesibility at a low temperature is improved for a glass surface, for example, polyolefin based resin film wrap. However, there is a problem that the adhesibility at a low temperature for a rough surface adherend, for example, a corrugated board, is not sufficient.
Therefore, a thermosensitive adhesive composition and a thermosensitive adhesive material have not been provided yet which have a sufficient adhesibility to a rough surface adherend, for example, a corrugated board, in an environment of from a low temperature (0° C.) to room temperature (25° C.) and have both an anti-blocking property and an adhesibility by which peeling-off can be prevented for an extended period of time. Currently, prompt provision thereof has been desired.